The mechanistic basis of neoplasia and carcinogenesis involves abnormal regulation of gene expression. RNA: protein interactions are important for all levels of gene expression (e.g. transcription, splicing, and translation). As a model system for studying RNA:protein interactions, the Williamson group is studying a complex of ribosomal protein S15 bound to 16S ribosomal RNA. The S15 protein is just one of the primary ribosomal binding proteins required for the assembly of the 30S ribosomal particle. The ribosomal protein S15 also regulates its own expression by binding to the 5'-untranslated region (5'-UTR) of its own messenger RNA and, consequently, reducing translation of S15 protein. The overall goal of this project is to understand the structural basis for the specific interactions of this 5'-UTR mRNA:S15 complex. Beginning with biochemical characterization of the 5'-UTR mRNA binding site for S15, a minimal site can be prepared for further study by NMR spectroscopy. Aiding in the NMR structure elucidation, specifically isotopically labeled ribonucleotides will be synthesized, thus simplifying the NMR spectra. The study of this 5'-UTR mRNA:S15 complex will provide contrast to studies of the 16S rRNA:S15 complex already underway in the lab. This research is significant for three reasons. 1) We will extend general knowledge about RNA:protein recognition. 2) Details about the particular interactions and conformation changes responsible for S15 recognition of two seemingly dissimilar RNAs will be learned. 3) New tools and strategies will be developed directed toward the study of large multicomponent complexes abundant in biology.